The Isle of Giants is an island that has been lost in time, home to primal devilsaurs, direhorns, and skyscreamers raised by the Zandalar tribe on the isle since the loss of Zandalar.
There is no "official" way to get to the isle: there are no introduction quests or NPCs to tell you about it.
Fly north from central Kun-Lai Summit on a flying mount through the fatigue waters to reach the Isle of Giants. On the Isle's southern side are two flight masters, one for the Alliance and one for the Horde. The isle is a no-fly zone and the Misty Shores in the waters before reaching the isle will dismount all comers.
If you do not have a class ability to navigate water faster, or a swimming mount, you may want to invest in an Anglers Fishing Raft or Reins of the Azure Water Strider from Anglers reputation.
The Isle is a volcanic, mountainous place, dominated by the large caldera dotted by steam pools in the center of the island. The southern beach is the only easy means of accessing the island's interior from the ocean, and thus the Horde, Alliance, and Zandalari all have landing sites there.
Zouchin Village, Kun-Lai Summit
Shrine of Seven Stars / Shrine of Two Moons, Vale of Eternal Blossoms
The isle is most likely based on the early alpha map draft for Mists of Pandaria, as it was pointed out as "Zandalari Isle". It was rumored the isle was moved to the position where the current Isle of Thunder is located, as before Patch 5.2 there was an entirely different, inaccessible isle located in its place, as detailed in the archives.
Thok the Bloodthirsty, a boss in the Siege of Orgrimmar, was found here and taken back to Orgrimmar by Garrosh Hellscream to be turned into a beast of war.
Where to start? Well, somebody would say all the way back to Warcraft I (aka Warcraft: Orcs & Humans or the First War), or maybe Warcraft II (aka Tides of Darkness or the Second War up to and including Wrath of the Lich King, Warcraft III is the best place to start. Also, this game then elicits more interesting questions. For instance, how Illidan Stormrage became so hated or where the Scourge started. You will learn all the history and geography of the Warcraft with our help and dedication.